The priority of a security interest is essentially the strength which the security interest has relative to other security interests and other interests in the same collateral.
Priority matters because upon enforcement of security interests by (for example) appointing a receiver to market and sell the collateral to repay secured obligations, the sale proceeds go first to satisfy the obligations secured by the highest priority security interest. If there is anything left after paying out the obligations secured by the highest priority security interest, the remaining proceeds go to the security interest with the next-highest priority, and so on. Priority is what the PPSA is all about – it is the “end game”. Priority determines most enforcement strategy, and who gets the value generated from enforcement.